Electrolytic hydrogenation and recovery of electrical energy



2 Sheets-Sheet 1 INVENTOR. STANLEY H. LANGER 5. H. LANGER A T TORNE Y Dec. 23, 1969 ELECTROLYTIC HYDROGENATION AND RECOVERY OF ELECTRICAL ENERGY Filed Aug. '7, 1967 s. H. LANGER 3,485,728

ELECTROLYTIC HYDROGENATION AND RECOVERY OF ELECTRICAL ENERGY Filed Aug. 7, 1967 2 Sheets-Sheet 2 STREAM H ALONE 0/? OTHER GASES VAR/ABLE RESISTOR POTENT/OMETER AMMETER UNSA TURA TED GA SEOUS COMPOUND l PRODUCT STREAM \HYDROGENATIOIV CELL INVENTOR. STANLEY H. LANGER A TTOR/VE Y nited States Patent 3,435,728 ELECTRULYTIC HYDROGENATION AND RECOVERY OF ELECTRICAL ENERGY Stanley Harold Langer, Madison, Wis., assignor to American Cyanamid Company, Stamford, Conn., a corporation of Maine Continuation-in-part of application Ser. No. 297,070, July 23, 1963. This application Aug. 7, 1967, Ser.

rm. (:1. B01k 1/00 U5. Cl. 204-73 Claims ABSTRACT OF THE DISCLOSURE This application relates to an improved process for hydrogenating an unsaturated hydrocarbon gas with attendant recovery of electrical energy which consists in the steps of: (a) passing a hydrogen-containing gas into a matrix hydrogenation cell as defined in FIGURE 2 of the drawing comprising a zone containing a catalytic, negatively-charged anode and a catalytic, positivelycharged cathode separated from one another by a matrix saturated with electrolyte, (b) electrically linking said anode and cathode in the absence of an imposed potential or added power, (c) passing resultant ionized hydrogen through the said matrix from the anode to the cathode, (d) contacting said cathode with impinging unsaturated hydrocarbon gas, (e) simultaneously effecting hydrogenation of the unsaturated hydrocarbon gas, and (f) recovering a good yield of saturated hydrocarbon gas and electrical energy.

This application is a continuation-in-part of my copending application for United States Letters Patent, Ser. No. 297,070, filed on July 23, 1963 and now abandoned.

The present invention relates to a novel process for hydrogenating unsaturated aliphatic compounds. More particularly, it relates to the hydrogenation of either gaseous olefinic or gaseous acetylenic compounds with attendant recovery of power. Still more particularly, the invention is concerned with the hydrogenation of gaseous olefins or acetylenic compounds at ambient temperatures and pressures in the absence of added power utilizing a matrix hydrogenation cell.

Hydrogenation of unsaturated compounds is indeed well known. In general, hydrogenation usually involves a reaction between an unsaturated compound and hydrogen carried out at elevated temperatures and pressures. To initiate the reaction, large surface contact of the unsaturated compound has been the usual practice. Another recognized procedure in effecting hydrogenation involves the electrolytic cathodic reduction of an unsaturated compound wherein hydrogen is evolved at the electrode by imposing a voltage thereon. This procedure, of course, entails the use of power. Unfortunately, none of the procedures presently known contemplates or permits the use of relatively small surface areas in the absence of added power. If a procedure could be found wherein these drawbacks can be overcome in a simple and straightforward, economical manner, such a method would be highly desirable and would constitute a distinct advance in the art.

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It is, therefore, an object of the present invention to provide a procedure whereby hydrogenation is accomplished in the absence of added power. It is a further object to provide a procedure whereby hydrogenation is carried out at ambient temperatures and pressures, utilizing relatively small surface areas wherein catalytic hydrogenation reaction takes place. These and other objects will become apparent from a reading of the following detailed description.

To this end, it has been found that hydrogen can be ionized readily whereby the ions are transported to a reaction site wherein an unsaturated hydrocarbon gas, such as an olefin or an acetylene, is present and simultaneously obtaining a saturated compound. Utilizing an electrolytic hydrogenation technique, more particularly defined hereinafter, power is generated rather than consumed during reaction.

In accordance with the process of the present invention, a hydrogenation cell comprising a catalytic anode, separated from a catalytic cathode by an electrolyte, preferably an acid electrolyte, is so constructed that the hydrogen or hydrogen-containing gas impinges on the anode resulting in hydrogen ions, and the latter are transported to the cathode through an acid electrolyte whereby reaction occurs at the anode in the presence of impinging unsaturated hydrocarbon gases such as, for instance, ethylene, propylene, butylene or acetylene. To effect reaction, it is necessary that the electrodes be electrically connected, for otherwise ionization of hydrogen with attendant release of electrons at the cathode cannot occur to obtain hydrogenation even though hydrogen ions are transported through the electrolytic medium. What is required is that electrons be transported from the anode through an external circuit to the cathode so as to provide for the completion of the hydrogenation process. Since the electrons are transported through an external circuit, power may be conveniently obtained while effecting control of the hydrogenation process in the cell.

One embodiment of the present invention comprises a hydrogenation cell which cell, in essence, is a gas-permeable container or membrane in contact with an electrolyte, such as aqueous phosphoric acid, aqueous alkaline, or a non-aqueous organic electrolyte, and a plurality of electrodes containing a catalytic agent in each. The electrodes are separated from each other by means of an electrolyte. External to the hydrogenation cell are wires connected to each of the electrodes so as to provide an external circuit.

In general, electrodes can be manufactured from carbon in which a noble or platinoid metal or other active metal has been incorporated. If desired, a catalyst per se such as, for instance, platinum or palladium can be emloyed in place of a carbon catalytic electrode. With respect to the manufacture of such catalytic electrodes, it is a good practice to employ waterproofing agents, such as polytetrafiuoroethylene, prior to the formation of the electrode to insure maximum contact of gas and electrolyte without causing flooding. For purposes of the present invention, electrodes can be made of the same material, or they may be made of dilferent :materials. However, it may be desirable to employ as the positive electrode a graphite carbon and platinum catalyst, while the negative electrode may simply contain lamp black and either a different active metal catalyst, such as paladium, or the same active metal catalyst in different quantities from the first.

The reactions occurring in the hydrogenation cell depend principally on the particular electrolyte employed. In essence, hydrogenation is found to be substantially proportional to the electricity generated. Reactions of the present process can be readily summarized in the following fashion:

In an acid electrolytic medium (1) at the anode: H 2H++2e (2) at the cathode:

2H++2e+RCH=CHR- RCH CH R In a base electrolytic medium:

(3) at the anode: H +2OH TH O+2e (4) at the cathode: 2H O+2e+RCH=CHR+ RCH CH R+ 2OH where R is either hydrogen or an alkyl group. In the above, illustrative electrolytes are, for instance: aqueous solutions comprising phosphoric acid, p-toluenesulfonic acid, aqueous sodium hydroxide, aqueous potassium hydroxide, or non-aqueous electrolyte, such as perchloric acid dissolved in acetonitrile. As stated previously, the acid electrolytes primary function is to insure that hydrogen ions formed at the oxidizing electrode or anode are transported to the opposite electrode or cathode. This is accomplished by providing for a drop in potential between the positive and negative electrode. The electrolyte is interposed between the catalytic electrodes. It may be employed either as a solid electrolyte, such as an ion exchange membrane, or as a liquid electrolyte. The latter can also be employed to saturate paper or other suitable membrane.

In FIG. 1 and FIG. 2 of the accompanying drawings which are merely exemplary and are to be taken as nonlimitative, there are shown two types of hydrogenation cells in cross-section, and in illustrative FIG. 3 there is shown schematically a total circuit for effecting the simultan eous hydrogenation of an unsaturated compound utilizing hydrogen gas alone or hydrogen admixed with other gases.

In the cell of FIG. 1, either a pure or an impure hydrogen gas stream enters inlet port 1 and passes into an electrically inert zone 2. The gas stream contacts a gaspermeable but a liquid-impermeable electrode 3 (anode), which acts as a separator and is fabricated from an active metal catalyst. Usually it includes additives, such as carbon and a waterproofing agent. An acid electrolyte 4 is provided so that hydrogen ions formed at the electrode 3 can be transported therethrough. Where gases other than hydrogen impinge on the anode, residual inert gases are withdrawn through a vent 5. Electrons that are also formed at the electrode 3 are transported by means of lead wire 6 to the negative electrode or cathode 7. Rate of transport of electrons is controlled by means of a variable resistor 6a and the overall reaction is monitored by ammeter 6b.

A preferred alternative hydrogenation cell shown as an exploded view in FIG. 2 is prepared by assembling the following elements: A membrane such as, for instance, a filter paper is saturated with electrolyte. TIhis membrane is designated as 11. Electrodes are represented by 12 and 13 and can be prepared by molding either a noble metal or a mixture of carbon and a noble metal with a waterproofing agent. Contacting the electrodes are metal screens 14 and 15 which are directly linked to an external circuit. Spacers composed of inert metal 16 and 17 are pressed directly against screens 14 and 15. Sealing gaskets 18 and 19 are provided to minimize leakage and the entire assembly is held in place by face plates 20 and 21. Either pure or impure hydrogen gas mixture enters through port 22 which ultimately flows to the electrode 12 and membrane 11 containing, for instance, 23% potassium hydroxide or phosphoric acid electrolyte. Since the electrode does not permit passage of any impure gas other than hydrogen therethrough, the impure gas is then exited through port 23. When contact of hydrogen is made at electrode 12 contiguous with an acidic medium, for instance, hydrogen ions are formed. These migrate through the electrolyte membrane 11 to the electrode 13 where they are discharged to effect in the presence of electrons hydrogenation of the unsaturated gas which entered port 24. Resultant desired product is discharged through port 25. The assembled elements are compressed and secured by bolts (not shown).

In FIG. 3, there is shown a schematic representation of a circuit comprising a hydrogenation cell 30, in which electrogenerative controlled hydrogenation occurs. There are also shown a potentiometer 31 and an ammeter 32 which conveniently allow the monitoring of voltage and current, respectively, through the cell thereby permitting variation in the rate of flow of hydrogen gas. Monitoring is accomplished by providing for increases or decreases in potential or voltage drop across the cell by adjusting an external resistor 33. Power can, if desired, be tapped off by means of leads 34 and 35 across the cell output. The variable resistor 33 allows for the control of voltage drop across the cell and consequently the control of passage of hydrogen ions through the cell is accomplished.

On one side of the hydrogenation cell a pure or impure hydrogen gas stream is permitted to flow through inlet port 36, and on the other side of the cell a stream of unsaturated hydrocarbon gas is introduced through the inlet port 37. Desired product is exited through port 38 and gases other than hydrogen are exited at port 39. The entire reaction can be terminated by opening switch 40.

In order to facilitate a further understanding of the invention, the following examples are presented primarily for purposes of illustrating more specific details thereof. The scope of the invention is not to be deemed limited thereby, except as defined in the claims. Unless otherwise stated, all parts and percentages are by weight.

EXAMPLE 1 An electrode sheet is formed by applying to a 200 mesh stainless steel screen a mixture of platinum (79.75%), colloidal silica (7.25%) and polytetrafluoroethylene (13%) to provide a total platinum loading of 32.7 milligrams per square centimeter and thereafter molding the supported electrode at 300 C. under a pressure of 320 pounds per square inch. The molded sheet is thereafter treated with 23% aqueous potassium hydroxide and washed several times with water.

Two electrodes are cut from the so-formed sheet and five discs of filter paper are next saturated with 6 N ph sphoric acid and then sandwiched between two formed electrodes. The electrodes are electrically connected through an external circuit in which a resistor, switch and ammeter are connected in series and a potentiometer c nnected in parallel With respect to the hydrogenation cell containing said electrodes. The active area of each electrode is 4.9 square centimeters. When ultimately assembled as shown in FIG. 2 and FIG. 3 of the drawing, the cell has an internal resistance of 1.02 ohms. Pure hydrogen is passed through one of the gas inlets and water-saturated ethylene is passed through an inlet port on the opposite side of the cell to yield an open circuit voltage of 0.44 volt as detected by the potentiometer.

The circuit is next closed and variations in voltage are noted while varying the current. Thus, at 0.8 milliampere, the voltage recorded is 0.33 volt; at 3.0 milliamperes, the voltage recorded is 0.21 volt; at 10.0 milliamperes, the voltage recorded is 0.17 volt; and at 50 milliamperes, the voltage recorded is 0.08 volt.

The cell is operated over a period of about one-hundred minutes at atmospheric pressure in a voltage range, of 0.04 volt to 0.14 volt and a current range of 5.6 milliamperes to 19.3 milliamperes to yield 54 coulombs of electricity. When the cell is operated batchwise, the hydrogen consumption or uptake is 7.55 milliliters which is equivalent to 58 coulombs. Although 54 coulombs of electricity are actually obtained, the difference or loss is apparently due to some leakage through the electrolyte. Further, desired product is analyzed and found to contain upon mass spectrometric analysis 28 percent ethane.

The hydrogenation cell as defined above, can be operated both batchwise and continuously, as desired. If the cell is to be operated continuously, there is no need for providing for shut-off valves connected to the outlet 38 of FIG. 3. However, when batchwise operation is contemplated, it is a good practice to provide for shut-off valve means both at inlet port 37 and outlet port 38 of FIG. 3.

EXAMPLE 2 A hydrogenation cell is prepared in accordance with the procedure set forth in Example 1 above. However, the cell is modified by saturating the electrolyte layer with 1 N p-toluenesulfonic acid in lieu of 6 N phosphoric acid. The cell resistance as measured by a 1000 cycle A.C. bridge is 0.66 ohm. The open circuit voltage, When all the gases, that is hydrogen and ethylene, flow respectively through each of the two sides of the cell, is found to be 0.40 volt.

In a closed circuit, the following voltages are obtained with predetermined varying currents:

TABLE I Voltage (volt): Current (milliamperes) The cell is operated for a period of two and one-half hours whereby 114 coulombs of electricity at voltages of 0.14 to 0.06 volt and currents of 13.8 to 6.7 milliamperes at room temperature under atmospheric pressure are obtained. When the system is operated statically, the volume of hydrogen consumed at room temperature and atmospheric pressure corresponds to a theoretical amount of electricity, namely 123 coulombs. However, the overall yield of electricity is found to be equal to 93 percent of the theoretical. The yield of ethane recovered corresponds to 96 percent of all the electricity generated.

EXAMPLE 3 Repeating the procedure of Example 1 in every respect, except that the hydrogenation cell is formed by utilizing a cationic exchange membrane in lieu of the acid-saturated membrane, the cationic exchange membrane is equilibrated with l N p-toluenesulfonic acid. The'internal resistance of the cell is 0.70 ohm and the open circuit voltage is 0.49 to 0.50 volt. The current is found to be 13 milliamperes at 0.15 volt with gases flowing through both sides of the cell.

EXAMPLE 4 Following the procedure of Example 2 in every respect, except that the platinum loading of one electrode on the hydrogen side is 20.4 milligrams per square centimeter and the platinum loading of the second electrode on the ethylene side is 2.2 milligrams per square centimeter supported on graphite, the cell possesses an internal resistance equal to 0.58 ohm. The open circuit voltage is 0.43 volt when gases are introduced on opposite sides of the cell.

In a closed circuit, the cell yields a current of 9.9 milliamperes at 0.17 volt, and 60 milliamperes at 0.1

volt.

EXAMPLE 5 Repeating the procedure of Example 1 in every detail, except that the cell is operated employing acetylene in lieu of ethylene, the cell yields an open circuit voltage of 0.36 volt and has an internal resistance of 1.34 ohms.

When the cell is operated on a closed circuit, it yields a current of 4 milliamperes at 0.05 volt. A mixture of both ethane and ethylene in a ratio of 1:2, respectively, is .obtained as the hydrogenation product.

EXAMPLE 6 Repeating Example 2 in every respect, except that butene-1 is employed in lieu of ethylene, the hydrogen cell has an internal resistance of 0.39 ohm and gives an open circuit voltage of 0.59 volt. When the circuit is closed, the cell is operated as summarized in Table II below.

TABLE II Voltage (volt): Current (milliamperes) 0.32 3.0 0.15 9.9 0.101 40.0 0.082 57.0

The hydrogen uptake or consumption as compared to electricity generated corresponds to 97 percent of the theoretical. On the butene side of the cell, mass spectrometric analysis indicates that 45 percent of the butene initially introduced is converted to butane.

EXAMPLE 7 A free electrolyte cell is constructed as shown in FIG. 1 above. This cell utilizes 1 N p-toluenesulfonic acid as the elctrolyte. The separating electrodes are platinum black supported on gas-porous Teflon sheet whereon 9.1 milligrams of platinum per square centimeter are deposited. Along with the platinum black, 10 percent by weight of polyethylene as an aqueous emulsion are applied as a water-proofing and binding agent. Propylene gas is introduced on one side of the cell and pure hydrogen is passed into the inlet port on the other side of the cell. The open circuit voltage is found to be 0.25 volt and when the circuit is closed, the cell performs as summarized in Table III below.

TABLE III Voltage (volt): Current (milliamperes) 0.20 1

The cell is operated for eight minutes at a potential of 0.084 volt and a current of 30 milliamperes. A portion of the outlet stream is analyzed by mass spectroscopy and is found to contain 2 percent propane indicating that hydrogenation occurs at substantially low potentials.

EXAMPLE 8 The free electrolyte cell of Example 7 is employed, except that the electrolyte is a 23 percent potassium hydroxide solution. Propylene gas is passed into one side of the cell and hydrogen gas is passed into the other side of the cell. The open circuit voltage is 0.24 volt and the cell performs in the manner indicated in Table IV below.

TABLE IV Voltage (volt): Current (milliamperes) 0.18 2 0.12 10 When operating the cell at a potential of 0.055 volt and a current of 25 milliamperes, a sample of the outlet stream on the propylene side of the cell is found to contain approximately 4 percent propane as determined by mass spectrometric analysis.

7 EXAMPLE 9 This example illustrates the use of an impure mixture of hydrogen gas.

An electrode sheet is formed by applying to a tantalum screen a mixture of platinum and 18 percent polytetrafluoroethylene to provide a total platinum loading of 9 milligrams per square centimeter. Thereafter, two electrodes are cut from the so-formed sheet and five discs of filter paper saturated with 1.7 N hydrofluoroboric acid are sandwiched between the two formed electrodes. The electrodes are then directly connected through an external circuit as in Example 1 above. The active area of each electrode is 4.9 square centimeters. When assembled as in FIG. 2 and FIG. 3 of the drawing, the cell has an internal resistance of 0.47 ohm.

A mixture of hydrogen (40 percent) and nitrogen (60 percent) is passed through one of the gas inlets on one side of the cell and propylene is passed through an inlet port on the opposite side of the cell yielding an open circuit voltage of 0.49 volt. The circuit is closed and the following data is observed as shown in Table V.

TABLE V Voltage (volt): Current (milliamperes) 0.18 2.3

The cell is next operated over a period of three hours in a voltage range of 003 volt to 0.12 volt and a current range of from 13 to 50 milliamperes, respectively, to yield 270 coulombs of electricity. When the cell is operated batchwise, i.e., by permitting a predetermined amount of unsaturated gas to be contacted with a predetermined amount of impure gas mixture introduced into the cell, the hydrogen consumption or uptake is 35.8 milliliters which is equivalent to 274 coulombs. Nothwithstanding the fact that 270 coulombs of electricity are obtained, the difference or loss is apparently due to leakage through the electrolyte. On spectrometric analysis, desired product analyzes as containing 77.8 percent propane.

EXAMPLE 10 One electrode sheet is formed by applying to a 50 mesh tantalum screen a mixture of platinum (79.75%), colloidal alumina (7.25%) and polytetrafluoroethylene (13%) to provide a total platinum loading of 9.0 milligrams per square centimeter, and thereafter molding the supported electrode at 300 C. under a pressure of 320 pounds per square inch. The molded sheet is thereafter treated with aqueous sulfuric acid and washed several times with water.

A second electrode sheet is prepared as above, except that a total palladium loading of 10.4 milligrams per square centimeter on a 200 mesh stainless steel screen is provided.

Two electrodes are then cut from each of the so-forrned sheets and five discs of filter paper are next saturated with 6 N phosphoric acid and sandwiched between the two out electrodes. The platinum electrode is positioned on the hydrogen side of the cell while the palladium electrode is positioned on the opposite side of the cell. The electrodes are directly connected through an external circuit in which a resistor, switch and ammeter are connected in serie and a potentiometer connected in parallel with respect to the hydrogenation cell containing said electrodes. The active area of each electrode is 4.9 square centimeters. When ultimately assembled as shown in FIG. 2 and FIG. 3 of the drawing, the cell has an internal resistance of 1.21 ohms as measured by an AC. bridge. Pure hydrogen is passed through one of the gas inlets and water-saturated propylene is passed through an inlet port on the opposite side of the cell to yield an open circuit voltage of 0.47 volt.

The circuit is next closed and variations in voltage are shown by varying the current. Thus, at 2.2 milliamperes, the voltage recorded is 0.22 volt; at 9.5 milliamperes, the voltage recorded is 0.18 volt; at 19.0 milliamperes, the voltage recorded is 0.15 volt; and at 45 milliamperes, the voltage recorded is 0.07 volt.

Similar results are obtained when employing palladium electrodes on both the propylene and hydrogen sides of the hydrogenation cell as defined in the example.

Although the process of the invention takes place at room temperature and atmospheric pressure, the process advantageously may take place at temperatures up to the boiling point or decomposition temperature of the electrolyte. In general, temperatures from about 25 C. to about C., or higher, and atmospheric pressure can be utilized. Additionally, as the gas-permeable but liquid impermeable electrode as hereinabove defined, there may be employed an unsintered, extensively fibrillated polytetrafluoroethylene structure as disclosed in a copending application, Ser. No. 522,964, filed on Jan, 25, 1966 by H. P. Landi. In that application, there is disclosed a process for preparing electrode structures by heating polymethylmethacrylate to a molten state, blending therein both olytetrafiuoroethylene in the form of finely divided particles as an aqueous dispersion and a conductive filler, cooling the blended mixture, pelletizing the latter and extruding the so-formed pellets directly into a sheet, treating the latter sheet with a suitable selective solvent for polymethylmethacrylate, extracting polymethylmethacrylate from said sheet and recovering an electrically-conductive, porous, self-supporting, unsintered, extensively fibrillated electrode structure.

I claim:

1. In a process for effecting electrogenerative, con trolled hydrogenation and the simultaneous recovery of residual power comprising; hydrogenerating an unsaturated hydrocarbon gas utilizing a hydrogen gas reactant by converting the latter electrolytically into hydrogen ions and electrons, the improvement which consists in the steps of:

(a) passing a hydrogen-containing gas into a first electrolyte-free zone which is not in contact with a matrix of a matrix hydrogenation cell comprising a catalytic. negatively-charged, non-electrolyte immersed anode and a catalytic, positively-charged, non-electrolyte immersed cathode separated from one another by a matrix saturated with electrolyte (b) electrically linking said anode and cathode in the absence of an imposed potential or added power (0) passing resultant ionized hydrogen through the said matrix from the anode to the cathode (d) electrolytically reducing hydrogen ions from the electrolyte at said cathode and (e) simultaneously depolarizing said cathode with unsaturated hydrocarbon gas supplied to said cathode and (f) recovering both a good yield of saturated hydrocarbon gas and electrical energy.

2. The process according to claim 1, in which the electrolyte in said matrix is phosphoric acid.

3. The process according to claim 1, in which the electrolyte in said matrix is potassium hydroxide.

4. The process according to claim 1, in which the catalytic electrode comprises a platinoid metal.

5. The process according to claim 1, in which the catalytic electrode comprises platinum.

6. The process according to claim 4, in platinoid metal is palladium.

7. The process according to claim 1, unsaturated hydrocarbon gas is ethylene.

8. The process according to claim 1, unsaturated hydrocarbon gas is propene.

9. The process according to claim 1, unsaturated hydrocarbon gas is butene-l.

which the in which the in which the in which the 9 10 10. The process according to claim 1, in Which the 3,124,520 3/1964 Juda 204-1.06 unsaturated hydrocarbon gas is acetylene. 3,180,762 5/1965 OsWin 13686 References Cited HOWARD s. WILLIAMS, Primary Examiner UNITED STATES PATENTS 5 H. M. FLOURNOY, Assistant Examiner 409,366 8/1899 MOWd et a]. 136-86 3,092,516 6/1963 Rightmire 136-86 US. Cl. X.R.

3,103,473 9/1963 Juda. 204-1.06 204--1 

